A cold rolled steel sheet used for shadow mask material has been manufactured by the following manufacture steps. That is, low carbon steel manufactured by a steel maker is performed by pickling and cold rolling so as to form a steel sheet having a predetermined thickness. After degreasing, the steel sheet is decarbonized and annealed in a wet atmosphere in a box type anneal furnace. Then, the steel sheet is secondary cold rolled so as to form a furnish steel sheet with a final thickness.
The cold rolled steel sheet manufactured by such a method is installed in a picture tube after performed by photo etching, annealing, pressing and baking. Unless carbon originally contained in the cold rolled steel sheet is decarbonized sufficiently during the above described steps, improper etching and improper press forming would be induced. Therefore, a content ratio of decarbonized and annealed carbon should be equal or less than 0.0015 wt %, preferably equal or less than 0.0008 wt %.
Regarding a cold rolled steel sheet used for a shadow mask manufactured by a method comprising the above described etching and press forming steps, it has been required that etching performance and press forming performance should be more stable than the conventional ones since a picture tube is required to provide high picture quality and improve its fine degree.
Japanese Patent Laid-open Publication No. Shou 56-139624, No. Hei 2-61029 and No. Hei 8-269627 discloses a method to resolve such a problem, respectively. In the above prior art, although steel components and annealing condition are described, these are not sufficient to provide stable etching performance and press forming performance in order to satisfy recent requirements with respect to the shadow mask material such as high picture quality and its fine improvement.
A purpose of the invention is to resolve the above described drawbacks in the conventional art and to provide shadow mask material with characteristic uniformly etched in a coil and press forming characteristic installed in a picture tube.